1. Field of the Invention
This invention is directed to devices for communicating between electrically isolated circuits using light signal transmission and fiber optic light guides.
2. Description of the Prior Art
Optical isolators for optically coupling electronically isolated circuits are known. Series C46 and C47 relays manufactured by Teledyne, Hawthorne, Calif. are one example. Typically, such relay devices enclose a light emitting diode (LED) and a photodiode in a standard DIP package, embedding the two diodes within the package in a manner to effect optical coupling. While such devices serve to optically isolate two electronic circuits and are compact, they are suited only for electrical isolation of circuits that can be mounted in close physical proximity. They are also unsuited for applications in which it is desirable to relay a signal simultaneously to two or more electrically isolated circuits.
Transmitters and receivers of optical signals for conversion to electrical signals using fiber optic light guides are also known. Light transmitted through a fiber optic light guide is typically characterized by relatively low dispersion upon leaving the end of the light guide. Conversely, a light guide will transmit only light directed toward its end from a relatively small angular area. Prior art devices for communicating between fiber optics and semiconductor diodes have frequently focused primarily on means for aligning a light source or receiver with a fiber optic light guide. For example, Simon, et al., U.S. Pat. No. 4,383,731, discloses a coupling between a semiconductor diode and a fiber optic light guide. Grafton, et al., U.S. Pat. No. 4,422,181, describes a bidirectional fiber optic coupler for communicating between semiconductor diodes.
Still other prior art devices are capable of both transmitting and receiving light through a fiber optic light guide to a single semiconductor device. For example, Geddes, Reissue No. 31,255, describes a fiber optic light guide simultaneously interfaced with both a light emitting region and a light detecting region of the same semiconductor device. Such devices can be used for bidirectional optical communication between circuits separated by widely varying distances but can operate in only one direction at any given time. These semiconductor devices operate to either detect or transmit light at any given time, but not both, and are incapable of optical communication between the photodetecting and photoemitting regions of the same semiconductor device. Further, the photodetecting and photoemitting components are in electrical communication at all times. Finally, such devices are not readily adaptable from one optically communicating and electrically isolating function to another.